Restate also stores a deployment version along with other invocation metadata. FaaS platforms like AWS Lambda make it very easy to retain old versions of your code, and Restate will complete a started invocation with the handlers that it started with. This way, you can "drain" older executions while new incoming requests are routed to the latest version.

You still have to ensure that all versions of handler code that may potentially be activated are fully compatible with all persisted state they may be expected to access, but that's not much different from handling rolling deployments in a large system.